Magnetic recording/reproduction apparatus with a long play mode

Abstract: A magnetic recording/reproduction apparatus of an azimuth system for recording/reproducing a digital signal by helical scanning a magnetic tape (8) has a SP mode and a LP mode having recording/reproducing time period N (N is an even number) times that of SP mode. The apparatus includes a pair of magnetic heads (7a, 7b) with opposite azimuth, disposed in close proximity on a circumferential face of a rotary head cylinder 5 with difference in level therebetween corresponding to a predetermined track pitch t for scanning simultaneously two continuous tracks at that pitch. The cylinder is rotated at the same rotation speed in both SP and LP modes, while the tape travel speed is reduced to 1/N that of SP mode when LP mode is specified. When LP mode is specified, the data amount of a digital signal to be recorded is compressed to 1/N that in SP mode, which are provided to the magnetic heads 2-channel record data, and the data amount of reproduced 2-channel digital signals of is expanded by N. In SP mode, recording/reproduction is carried out by every 2 continuous tracks by the pair of magnetic heads for every 1 rotation of the cylinder. In LP mode, recording/reproduction is carried out in a unit of 2 continuous tracks by the pair of magnetic heads for every N rotations of the cylinder.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording/reproduction apparatus including a long play mode, and more particularly, to a helical scan system magnetic recording/reproduction apparatus that can record and/or reproduce analog or digital information in a long play mode in addition to a standard play mode. Description of the Background Art In the field of conventional digital magnetic recording/reproduction apparatuses that record and/or reproduce digital information using a helical scan and azimuth recording/reproduction system, research efforts are expended on employing a long play mode (referred to as LP mode hereinafter) in addition to the standard play mode (referred to as SP mode hereinafter) as recording/reproduction modes. The potential of such a long play mode is discussed in, for example, "A Study on Long Time Mode Recording for Home Use Digital VTR", Proceedings of National Conference of Institute of Electronics, Information and Communication Engineers of Japan, 1-382, Spring, 1990. In such a digital magnetic recording/reproduction apparatus, recording and reproduction of high definition television broadcasting having a great amount of information is desired in addition to the recording and reproduction of the current NTSC system and PAL system television broadcasting. However, a specific structure is not yet known for realizing both the SP mode and the LP mode, or for recording/reproducing various broadcasting differing in amount of information by a conventional digital magnetic recording/reproduction apparatus. A conventional digital magnetic recording/reproduction apparatus generally has two magnetic heads 2a and 2b with opposite azimuth mounted on the circumferential face of a rotary head cylinder 1, at locations apart by 180° from each other, as shown in Fig. 1. The attached manner of the magnetic heads to a cylinder is basically similar to that in a VTR of a general VHS system. In the drawing, the positive symbol "+" indicates the azimuth of head 2a (referred to as azimuth A hereinafter), and the negative symbol "-" indicates the azimuth of head 2b (referred to as azimuth B hereinafter). According to the structure shown in Fig. 1, heads 2a and 2b helical-scan a magnetic tape (not shown) alternately for each half rotation of cylinder 1 by rotating cylinder 1 at a constant speed while winding and running the magnetic tape around cylinder 1 at a predetermined angle in recording/reproduction operation. Particularly in a recording/reproduction operation of the SP mode, the travel speed of the tape is controlled so that the scanning position of the head on the magnetic tape is shifted by every predetermined one track pitch substantially corresponding to the width of the head. In response to a rotation detection pulse (referred to as RF pulse) of high frequency in synchronization with the rotation of cylinder 1, generated by a detection means not shown, heads 2a and 2b are alternately selected as recording or reproducing heads for every half rotation of cylinder 1. As a result, in a recording operation of a SP mode, a track 4a of azimuth A and a track 4b of azimuth B are alternately formed on a magnetic tape 3 with a predetermined track pitch t for each half rotation of cylinder 1 in response to the RF pulse, whereby a plurality of blocks of record data D1, D2, D3, ..., each corresponding to half rotation of cylinder 1, i.e. corresponding to 1 track, are continuously recorded on the formed plurality of tracks, as shown in Fig. 2. The arrows a and b in Fig. 2 indicate the tape travel direction and the head scanning direction, respectively. When the data to be recorded has a great amount of information such as video and audio data, the data to be recorded is compressed to several times smaller than the original amount of data by high efficiency coding, and then recorded. A digital magnetic recording/reproduction apparatus is envisioned including, in addition to the above-described SP mode, a long play mode that realizes a recording and reproducing time period N times that of the SP mode. In order to realize recording and reproduction in a LP mode that is N times the recording and reproducing time period of a SP mode, basically it is necessary to reduce the tape travel speed in the LP mode to 1/N the tape travel speed of the SP mode. This also applies to the case of the so-called EP mode of a VHS system VTR. Assuming that the rotation speed of a cylinder is maintained at a speed identical to that of the SP mode while the tape travel speed is reduced to 1/N of that in the SP mode in a conventional digital magnetic recording/reproduction apparatus, tracks will be formed in a sequentially overwritten manner, whereby the track pitch in the recording/reproduction operation of a LP mode is narrowed to 1/N the track pitch of a SP mode. In other words, the track density on a tape in a LP mode becomes N times that in the SP mode to reduce the level of a signal reproduced from each track. This leads to reduction of the S/N ratio of recording and reproduction in the LP mode. A possible consideration is that the track pitch formed on a tape in a LP mode can be maintained identical to that of the SP mode by compressing the amount of data of the information to be recorded/reproduced at a data compression rate N times that of the SP mode to reduce the original amount of information to 1/N, and by reducing the tape travel speed and the rotation speed of the cylinder to 1/N those of the SP mode. For example, using the heads of the structure shown in Fig. 1, if the tape speed and the rotation speed of cylinder 1 are reduced to 1/N those of the SP mode in the recording and reproducing operation of a LP mode, the track pattern on a magnetic tape will be scanned at a predetermined track pitch t for every half rotation of cylinder 1, similar to the track pattern in the SP mode of Fig. 2. However, the above-described structure requires a change of the rotation speed of the cylinder in response to switching between the SP mode and the LP mode, giving rise to a problem that a complex control system is needed. Because the relative speed between the tape and the head in a recording and reproducing operation is significantly lower in the LP mode than in the SP mode, the level of a signal reproduced in the LP mode is greatly reduced to also lower the frequency thereof (1/N). It is therefore necessary to broaden the characteristics of reproduction circuitry such as electro-magnetic conversion system and waveform equalization to wide band characteristics that covers frequency as low as 1/N in comparison with the circuitry characteristics where only the SP mode is assumed. Because the output level of a signal reproduced in a LP mode is greatly degraded as described above, the S/N ratio of a reproduced output of head is significantly reduced. An approach to solve these problems could be taken by setting the rotation speed of the cylinder to 1/N the rotation speed of the SP mode only during a recording operation of the LP mode, and setting the rotation speed of the cylinder to two times that of the reproducing operation, i.e. equal to that of the SP mode, in a reproducing operation of the LP mode. However, in such a case, a magnetic head of a width sufficiently wider than the track pitch must be used to properly trace the track formed on the tape in a reproducing operation. Furthermore, a complex control system is required to control the switching of the rotation speed of the cylinder and for controlling tracking. Thus, various disadvantages are generated when recording and reproduction is to be carried out at a track pitch identical to that of the SP mode in a LP mode in a conventional digital magnetic recording/reproduction apparatus. If the cylinder rotation speed in a LP mode is maintained identical to that of a SP mode while reducing only the tape travel speed to 1/N of that of the SP mode to solve these disadvantages, the track pitch becomes 1/N that of the SP mode to reduce the level of a reproduced signal, as described before. An approach as set forth in the following is considered to solve the above-described problems while maintaining the rotation speed of the cylinder at the same speed. For the sake of simplicity, a case where the recording/reproducing time period of a LP mode is set to two times that of a SP mode, i.e. N=2, will be described in the following. In a LP mode, it is assumed that the tape travel speed is reduced to 1/2 of that in the SP mode while maintaining the rotation speed of the cylinder equal to that of a SP mode. The above-described problems of increasing the complexity of the cylinder rotation control and change in the reproduced signal characteristics can be eliminated by a structure in which the scanning position of the head on a tape is not shifted by each track pitch t for every half rotation of cylinder 1 as in a SP mode, but shifted by a track pitch t for every one (=N/2) rotation of cylinder 1. However, the head used for recording and reproduction will be limited to either head 2a or 2b, in other words, only a track of either azimuth A or B is formed on the tape. This means that recording and reproduction of the azimuth system cannot be carried out. In order to enable an azimuth system recording/reproducing operation, an intermittent recording and reproduction operation can be considered wherein recording/reproduction of two tracks is carried out by heads 2a and 2b during a rotation of cylinder 1, recording/reproduction is not carried out during the next rotation, and recording/reproduction of two tracks is carried out by heads 2a and 2b during a second next rotation of cylinder 1. Fig. 3 shows a track pattern on a tape 3 according to such an intermittent operation. Since the rotation speed of cylinder 1 is identical to that of the SP mode in the example shown in Fig. 3, the frequency of the RF pulse is identical to that of the RF pulse in the LP mode of Fig. 2. In Fig. 3, each of record data blocks D1', D2', D3', ... is the data of each of record data blocks D1, D2, D3, ... of the SP mode of Fig. 2 having the amount of data compressed to 1/2 and recorded on each track by every 2 blocks. The period of a RF pulse illustrated by the hatched region in Fig. 3 indicates an idle period where the above-described recording/reproduction is not carried out. Although recording/reproduction in an azimuth system using heads 2a and 2b is possible according to the structure shown in Fig. 3, a track of azimuth B will be overwritten on a track of azimuth A. Therefore, the pitch of the track of azimuth A is narrowed to 1/2, so that the track pitch of a LP mode cannot be maintained identical to that of a SP mode. The above-described various problems are expected to occur, not only in a magnetic recording/reproduction apparatus carrying out recording and reproduction in digital system, but also in a magnetic recording/reproduction apparatus of an analog system. For example, the problem of the track pitch formed on a tape being narrowed in a LP mode to reduce the S/N ratio due to the aforementioned reason will also occur in a helical scan system magnetic recording/reproduction apparatus such as a conventional VHS system VTR or 8mm VTR that carries out analog recording/reproduction. There is also a problem that the mechanical accuracy of the mechanism of the magnetic head and the rotary cylinder must be extremely critical in order to ensure compatibility in a LP mode between different apparatuses. DE-A-3819393 discloses a helical scan VTR for digital signals having a standard play and a long play mode. The rotary head drum carries two pairs of magnetic heads. The heads of each pair are in close proximity to each other and have a difference in level on the circumference of the head drum corresponding to a predetermined track pitch. In the LP-mode (with recording duration twice as long as in the SP-mode) the signal is only recorded by two of the heads. The heads of the other pair have only a function in the SP-mode. SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording/reproduction apparatus that realizes a LP mode having favorable signal recording/reproduction characteristics with a simple structure. Another object of the present invention is to provide a magnetic recording/reproduction apparatus that can carry out recording/reproduction of a LP mode at a track pitch identical to that of a SP mode. A further object of the present invention is to provide a magnetic recording/reproduction apparatus that has narrowing of a track pitch on a tape in a LP mode prevented and the S/N ratio of a reproduced signal improved. Still another object of the present invention is to provide a magnetic recording/reproduction apparatus that eliminates the necessity of complex control for switching the cylinder rotation speed by maintaining the rotation speed of a rotary head cylinder in a recording/reproduction operation of a LP mode identical to that of a SP mode. A still further object of the present invention is to provide a magnetic recording/reproduction apparatus that eliminates the necessity of altering the recording/reproduction circuit characteristics for a recording/reproduction operation of a LP mode. Yet a further object of the present invention is to provide a magnetic recording/reproduction apparatus that can carry out azimuth system recording/reproduction in a recording/reproduction operation of a LP mode. Yet another object of the present invention is to provide a magnetic recording/reproduction apparatus that allows recording/reproduction of various broadcasting differing in the amount of information. The above objects are achieved by a magnetic recording/reproduction apparatus of a azimuth system according to claim 1. The dependent claims are related to further advantageous aspects of the present invention. The main advantage of the present invention is to improve the S/N ratio of a reproduce signal in a long play mode by carrying out recording/reproduction of the long time mode at a track pitch identical to that of the standard play mode. Another advantage of the present invention is to eliminate the need of complex control for switching the speed of the rotary head cylinder by maintaining the rotation speed of the rotary head cylinder in the long play mode identical to that of the standard play mode. A further advantage of the present invention is to eliminate the need of altering circuitry characteristics for recording/reproduction in a long play mode by maintaining the rotation speed of the rotary head cylinder in the long play mode identical to that of the standard play mode. Still another advantage of the present invention is to allow azimuth system recording/reproduction while maintaining the track pitch in the long play mode identical to that of the standard play mode. A still further advantage of the present invention is to allow recording/reproduction of various broadcasting differing in the amount of information while maintaining the track pitch in the long play mode identical to that of the standard play mode. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view schematically showing a head arrangement of a conventional magnetic recording/reproduction apparatus. Fig. 2 shows a track pattern in a SP mode of a conventional magnetic recording/reproduction apparatus. Fig. 3 shows a presumption of a track pattern in a LP mode of a magnetic recording/reproduction apparatus. Fig. 4 is a block diagram schematically showing an example of a magnetic recording/reproduction apparatus not belonging to the present invention. Fig. 5 is a plan view schematically showing the head arrangement of the example. Fig. 6 is a front view schematically showing the head arrangement of the example. Fig. 7 shows a track pattern in a SP mode of the example. Fig. 8 shows a record data arrangement in a SP mode of the example. Fig. 9 shows a track pattern in a LP mode of the example. Fig. 10 shows a record data arrangement in a LP mode of the example. Fig. 11 is a block diagram schematically showing a magnetic recording/reproduction apparatus according to the present invention. Fig. 12 is a front view schematically showing a head arrangement of the invention. Fig. 13 shows a track pattern in a SP mode of the invention. Fig. 14 shows a record data arrangement in a SP mode of the invention. Fig. 15 shows a track pattern in a LP mode of the invention. Fig. 16 shows a record data arrangement in a LP mode of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 4, a magnetic recording/reproduction apparatus according to an example (not covered by the invention) includes a rotary head cylinder 5 rotating in the direction of arrow "b", having a double azimuth head 6 mounted on the circumferential face thereof. More specifically, double azimuth head 6 includes a pair of magnetic head units 7a and 7b disposed in close proximity as shown in the plan view of Fig. 5. Magnetic head unit 7a has an azimuth A, and magnetic head unit 7b has an opposite azimuth B, similar to those of magnetic heads 2a and 2b shown in Fig. 1. The two magnetic head units 7a and 7b are disposed in close proximity with a difference in level therebetween in the rotating axis direction corresponding to one track pitch t predetermined in advance according to the format, as shown in Fig. 6. The head width of magnetic head units 7a and 7b may be equal or different from each other. By a pair of tape guides 9a and 9b provided in the proximity of rotary head cylinder 5, a magnetic tape 8 is wound around rotary head cylinder 5 over an angle of, for example, 180°, to travel in the direction of arrow "a" in a recording/reproduction operation by a capstan motor 10 rotating in the direction of arrow "c". A mode signal is provided from a system controller (not shown) controlling the entire magnetic recording/reproduction apparatus to a mode terminal 11 specifying whether recording/reproduction in a SP mode or a LP mode is to be executed. The mode signal provided to mode terminal 11 is applied to a capstan motor driving unit 12, a recording and reproducing processing unit 15, and a head control unit 17. Capstan motor driving unit 12 controls the drive of capstan motor 10 according to the mode signal. A video signal to be recorded is provided from a video signal processing unit (not shown) to a record video terminal 13. The video signal to be recorded provided to terminal 13 is applied to recording and reproducing processing unit 15 which is controlled by the above-described mode signal. Recording and reproducing processing unit 15 digitally converts a video signal to be recorded and carries out time base compression thereon in a recording operation, and applies a time base expansion on data reproduced by double azimuth head 6 to convert the same into analog data in a reproduction operation. A sensor 16 is provided in the proximity of rotary head cylinder 5 for detecting the phase and the frequency of the rotation of rotary head cylinder 5. Head control unit 17 includes a rotation detection circuit 18, a timing control circuit 20, and a pair of head selection switches 19a and 19b. According to an output of sensor 16, rotation detection circuit 18 forms RF pulses in synchronization with the rotation of rotary head cylinder 5 to provide the pusles to timing control circuit 20. According to this RF pulses and the mode signal provided from mode terminal 11, timing control circuit 20 controls the pair of head selection switches 19a and 19b to open/close simultaneously the connection between the 2 channel outputs A and B of recording and reproducing processing unit 15 and the pair of magnetic head units 7a and 7b forming double azimuth head 6. Rotary head cylinder 5 is driven by a cylinder motor (not shown) to rotate in the direction of arrow "b" at the same rotation speed regardless of which mode of SP or LP is specified. Although the present invention generally relates to a magnetic recording/reproduction apparatus that has a SP mode and a LP mode having the recording/reproduction time period N (N is an even number) times that of the SP mode as recording/reproduction modes, the following embodiments will be described in which N is being set as N=2 for the sake of simplification. When a mode signal specifying the SP mode is applied to mode terminal 11, capstan motor driving unit 12 causes tape 8 to run in the direction of arrow "a" at a constant speed such that the scanning position of the pair of head units 7a and 7b on tape 8 is shifted by a predetermined one track pitch t for every half rotation of rotary head cylinder 5. When a mode signal specifying the LP mode is applied to mode terminal 11, capstan motor driving unit 12 reduces the travel speed of tape 8 to 1/2 the travel speed of the SP mode. Because head units 7a and 7b are attached to rotary head cylinder 5 with difference in level therebetween corresponding to a track pitch t as shown in Fig. 6, two continuous tracks each having a width of track pitch t on tape 8 are simultaneously scanned in parallel during a period corresponding to approximately half a rotation in every one rotation of rotary head cylinder 5. The recording or reproducing operation in the SP mode will first be described. Since the scanning position on tape 8 by the pair of head units 7a and 7b is shifted by one track pitch t for every half rotation of rotary head cylinder 5 as described above, the scanning position is shifted by 2 track pitches in the SP mode. In a recording operation of the SP mode, a track 21a of azimuth A and a track 21b of azimuth B each having a width of one track pitch t are alternately formed as shown in the track pattern of Fig. 7 by the simultaneous parallel scanning in the unit of 2 tracks by the pair of head units 7a and 7b mounted on rotary head cylinder 5. Since head units 7a and 7b scan tape 8 during a period corresponding to a half rotation in every one rotation of rotary head cylinder 5 as described above, timing control unit 20 simultaneously closes the pair of head selection switches 19a and 19b to simultaneously select head units 7a and 7b as recording or reproduction heads during half a period of a RF pulse from rotation detection circuit 18. In the recording operation, recording and reproducing processing unit 15 digital-converts a video signal to be recorded from terminal 13, whereby a plurality of record data blocks D1, D2, D3, ... each corresponding to half a rotation of rotary head cylinder 5, i.e. corresponding to one track on tape 8, are formed in time sequence as shown in Fig. 8, similar to the record data of the prior art shown in Fig. 2. Identifying the data recorded/reproduced by the pair of head units 7a and 7b as data of channel A and channel B, respectively, recording and reproducing processing unit 15 alternately distributes the plurality of data blocks D1, D2, D3, ... as data of channel A and channel B as shown in Fig. 8 to output the same in parallel at the same time during the half rotation period, where switches 19a and 19b are simultaneously closed, of each rotation of rotary head cylinder 5. In Fig. 8, τ indicates one rotation period of rotary head cylinder 5, i.e. one period of a RF pulse, and ℓ indicates the amount of record data. As described above, record data D1 and D2, D3 and D4, ..., each having an amount of data corresponding to one track, are recorded simultaneously and in parallel on two continuous tracks 21a and 21b of azimuth A and B, respectively, on tape 8 during half a rotation of every one rotation of rotary head cylinder 5 by the pair of head units 7a and 7b. As a result, a track pattern of an azimuth recording system each having a width of one track pitch t is continuously formed on tape 8, similar to that of the conventional case shown in Fig. 2. Next, a recording or reproduction operation in a LP mode having a recording/reproduction time period two times that of the SP mode will be described. In the LP mode, the rotation speed as that of rotary head cylinder 5 is maintained at the same rotation speed of the SP mode, while the travel speed of tape 8 is reduced to 1/2 the travel speed of the SP mode. According to this reduction of the tape travel speed, the scanning position on tape 8 by the pair of head units 7a and 7b is shifted by one track pitch t for every one rotation of rotary head cylinder 5, which is half the 2 track pitch 2t in the above-described SP mode. Similar to the above-described SP mode of Fig. 7, timing control unit 20 simultaneously closes switches 19a and 19b during a period corresponding to one rotation of every 2 rotations of rotary head cylinder 5 by which the head scanning position on tape 8 is shifted by 2 track pitches 2t to simultaneously select head units 7a and 7b as record heads or reproduction heads in order to maintain the width of each track scanned by magnetic head units 17a and 17b at one track pitch t when the LP mode is specified. By such a recording/reproduction in the unit of 2 tracks b by head units 7a and 7b for every 2 rotations of rotary head cylinder 5, track 21a of azimuth A and track 21b of azimuth B, each having a width of one track pitch t, are alternately scanned on tape 8 as shown in the track pattern of Fig. 9 in the recording/reproduction operation of the LP mode. Since the tape travel speed in the LP mode is reduced to 1/2 the tape travel speed of the SP mode, the recording or reproduction of one track 21a or 21b on tape 8 requires 2 (=N) times the time period of the SP mode. Therefore, the stored amount of information on tape 8 is reduced to 1/2 (=1/N) that of the SP mode. In a recording operation of the LP mode, recording and reproducing processing unit 15 thins down each data of record data blocks D1, D2, D3, ... to compress the time base thereof to 1/2, whereby a plurality of record data blocks D1', D2', D3', ... having the amount of information reduced to half are formed in time sequence, as shown in Fig. 10. Recording and reproducing processing unit 15 alternately distributes the formed data blocks in a unit of combination of two continuous data blocks such as D1'+D2', D3'+D4', D5'+D6', ... as the record data of 2 channels of A and B to output the same in parallel at the same time during one rotation period, where switches 19 a and 19b are closed, of every 2 rotations of rotary head cylinder 5. More specifically, the record unit of each channel, for example, each of D1'+D2', D3'+D4', D5'+D6', ... has an amount of information compressed to that of one track. The data of 2 channels provided in parallel from recording and reproducing processing unit 15 as shown in Fig. 10 are simultaneously recorded as shown in Fig. 9 as two continuous tracks of azimuth A and azimuth B, each having a width of one track pitch t on tape 8, intermittently for every other rotation of cylinder 5. The frequency of RF pulses in the LP mode of Fig. 9 is identical to that of the RF pulses in the SP mode of Fig. 7. "ℓ/2" in Fig. 10 indicates the amount of data of each of record data blocks D1', D2', ..., implying that each is half the data amount "ℓ" of each of record data blocks D1, D2, ... of Fig. 8. In Fig. 9, the period of a RF pulse indicated by a hatched region implies an idle period where recording/reproduction is not carried out. In a reproduction operation of the SP mode, switches 19a and 19b are closed during a period corresponding to half a rotation of each one rotation of cylinder 5 by timing control unit 20, similar to a recording operation in the SP mode. In a reproduction operation of the LP mode, switches 19a and 19b are closed during a period corresponding to one rotation of every 2 rotations of cylinder 5, similar to a recording operation of the SP mode. In either case, data reproduced from two continuous tracks 21a and 21b simultaneously scanned by head units 7a and 7b are provided to recording and producing processing unit 15 as data of 2 channels of A and B during the time period when switches 19a and 19b are closed. Recording and reproducing processing unit 15 applies a time base expansion and analog-conversion, opposite to those at the time of recording, on reproduced signals, which are provided from terminal 13 as a reproduced video signal of one channel. Although the above example was described in which N is set as N=2, the present invention is applicable to the case where N is an even number other than 2. According to the above-described example, two continuous tracks on a tape are scanned simultaneously for every one rotation of a rotary head cylinder by a double azimuth head 6 having a difference in level between head units corresponding to a predetermined track pitch t. As a result, in a SP mode, the head scan position on tape 8 is shifted by 2 tracks for every one rotation of rotary head cylinder 5 to carry out scanning in the unit of 2 tracks by a pair of head units 7a and 7b opposite in azimuth, so that an azimuth system recording/reproduction is allowed with a track pattern of a the predetermined track pitch. In a LP mode having a recording/reproduction time period N times that of the SP mode, scanning by head units 7a and 7b is carried out in the unit of 2 tracks for every shifting of the head scanning position by two tracks on magnetic tape 8 by N rotations of rotary head cylinder 5, allowing an azimuth system recording/reproduction with a track pattern of a track pitch identical to that of the SP mode. By maintaining the rotation speed of rotary head cylinder 5 identical to that of the SP mode while reducing only the travel speed of tape 8 to 1/N in the LP mode, an azimuth recording/reproduction is possible with a track pitch identical to that of the SP mode. Therefore, the track pitch is prevented from being narrowed in the LP mode. This prevents reduction in the reproduced output as well as the deterioration of the S/N ratio in the LP mode. Furthermore, the drive control of rotary head cylinder will not become complicated. Because the rotation speed of rotary head cylinder 5 is maintained equal to that of the SP mode even in the LP mode, the recording and reproducing circuitry characteristics in the LP mode does not have to be changed to those adapted for a band wider than that of the SP mode. The present invention will be described hereinafter with reference to Fig. 11. Fig. 11 is similar to the example shown in Fig. 4 except for the points set forth in the following. Therefore, description of common elements will not be repeated. A double azimuth head 6' mounted on the circumferential face of a rotary head cylinder 5 includes a pair of magnetic head units 7a' and 7b' provided with no difference in level therebetween, as shown in Fig. 12. A single-channel recording and reproducing processing unit 15' is provided instead of 2-channel recording and reproducing processing unit 15 of Fig. 4. Furthermore, instead of timing control unit 20 and the pair of switches 19a and 19b of Fig. 4, a mode switch 22, a head selection switch 23, a timing control circuit 24 controlling the open/close of mode switch 22, and a selection control circuit 25 for controlling the open/close of head selection switch 23 are provided as components constituting head control unit 17. Since head units 7a' and 7b' with opposite azimuth A and B are mounted on rotary head cylinder 5 with no difference in level, the pair of head units 7a' and 7b' helical-scan the same track on tape 8 successively for every one rotation of rotary head cylinder 5. If the constant tape travel speed in a SP mode and a LP mode is identical to that of the first embodiment, the scanning position of head units 7a' and 7b' is shifted by every 2 track pitches 2t for every one rotation of rotary head cylinder 5 when in a SP mode. In the present invention, the rotation speed of rotary head cylinder 5 is set to two times that of the first embodiment, so that the scanning position of head units 7a' and 7b' is shifted by one track pitch t for every one rotation of rotary head cylinder 5 in the SP mode. Because head units 7a' and 7b' are selected alternately to record or reproduce data of one track for every one rotation of rotary head cylinder 5 in a recording or reproduction operation of the SP mode, timing control circuit 24 closes switch 22 during a period which is approximately half a rotation of every one rotation of rotary head cylinder 5. Head selection control circuit 25 alternately switches the moving contact of switch 23 between a contact 23a of the head 7a' side and a contact 23b of the head 7b' side for every one rotation of rotary head cylinder 5. In a recording operation of the SP mode, recording and reproducing processing unit 15' digital-converts a video signal provided from terminal 13 to sequentially output a plurality of record data blocks D1, D2, D3, ..., each corresponding to one rotation of rotary head cylinder 5, i.e. one track on tape 8. In Fig. 14, τ' indicates the period of one rotation of rotary head cylinder 5, corresponding to 1/2 the period τ of the example. In a recording operation of the SP mode, a track 21a of a width of one track pitch t of azimuth A and a track 21b of a width of one track pitch t of azimuth B are alternately formed by head units 7a' and 7b', respectively, for every one rotation of rotary head cylinder 5, as shown in Fig. 13. As a result, a track pattern identical to that of the example of Fig. 7 is formed on tape 8. In a LP mode having a recording/reproduction time period 2 times that the SP mode, the travel speed of magnetic tape 8 is reduced to 1/2 the tape travel speed of the SP mode, while the rotation speed of rotary head cylinder 5 is the same as in the SP mode, similar to the above-described example. As a result, the scan position on tape 8 by the pair of head units 7a' and 7b' is shifted by one track pitch t for every 2 rotations of rotary head cylinder 5 as shown in Fig. 15. In the SP mode, switch 22 is controlled by timing control circuit 24 to be closed during a period corresponding to half a rotation of every other rotation of rotary head cylinder 5. Switch 23 is controlled by head selection control circuit 25 to be alternately switched between contacts 23a and 23b for every 2 rotations of rotary head cylinder 5. Recording and reproducing processing unit 15' compresses, the time base of record data blocks D1, D2, D3, ... of Fig. 14 to form and output a plurality of data blocks D1', D2', D3', ... each having the amount of data reduced to 1/2, as shown in Fig. 16. The output plurality of recording data blocks are alternately distributed as a combination of record data blocks D1'+D2' as the data of channel A, D3'+D4' as data of channel B, ... for each one rotation of every other rotation of rotary head cylinder 5 to be provided to the pair of head units 7a' and 7b' by switch 23. In a recording operation of the LP mode, a track 21a of a width of one track pitch t of azimuth A and a track 21b of a width of one track pitch t of azimuth B are alternately formed on tape 8 by head unit 7a' and head unit 7b', respectively, for each one rotation of every other rotation of rotary head cylinder 5, as shown in Fig. 15. As a result, a track pattern identical to that of the first embodiment of Fig. 9 is formed on tape 8. Thus, according to the invention, the same track on tape 8 is helical scanned sequentially for every one rotation of rotary head cylinder 5 by a double azimuth head 6' including a pair of magnetic head units 7a' and 7b' mounted on rotary head cylinder 5 with no difference in level. In the SP mode, the head scan position on tape 8 is shifted by one track pitch for every one rotation of rotary head cylinder 5, whereby head units 7a' and 7b' are selected alternately for every one rotation of rotary head cylinder 5. Therefore, an azimuth system recording/reproduction is allowed with a track pattern of the predetermined track pitch. In the LP mode having a recording/reproduction time period N times that of the SP mode, head units 7a' and 7b' are alternately selected for every one track pitch shift of the head scan position on tape 8 for every N rotations of rotary head cylinder 5, similar to the SP mode. Therefore, an azimuth system recording/reproduction is allowed with the track pattern of the track pitch identical to that of the SP mode. According to the invention, the tape travel speed is reduced to 1/N the tape travel speed of a SP mode while maintaining the rotation speed of rotary head speed 5 identical to that of a SP mode, so that an azimuth recording/reproduction is allowed while maintaining a track pitch identical to that of the SP mode. Therefore, an effect similar to that of the above-described first embodiment can be obtained. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A magnetic recording/reproduction apparatus of an azimuth system for recording and/or reproducing a digital signal by helical-scanning a magnetic tape (8), including a standard play mode and a long play mode of a recording and reproducing time period N times that of said standard play mode, as recording and reproducing mode, said magnetic recording/reproduction apparatus comprising: mode specifying means (11) for specifying one of said standard play mode and said long play mode to be executed, a rotary head cylinder (5) driven to rotate at the same rotation speed in either of said standard play mode and said long play mode, one pair of magnetic heads (7a', 7b') having opposite azimuth, disposed in close proximity on a circumferential face of said rotary head cylinder with no difference in level therebetween, whereby both heads scan continuously the same track on said magnetic tape for every one rotation of said rotary head cylinder, tape speed control means (10, 12) for reducing the travel speed of said magnetic tape running while being wound around said rotary head cylinder to 1/N the travel speed of said standard play mode when said long play mode is specified, signal processing means (15') for compressing the amount of data of a digital signal to be recorded to 1/N the amount of data of the standard play mode, and/or expanding the amount of data of a reproduced digital signal by N times, when the long play mode is specified, and head control means (16, 17) for alternately driving said pair of magnetic heads to carry out recording or reproduction in a unit of one track on said magnetic tape, for every one rotation of said rotary head cylinder when said standard play mode is specified, and for every N rotations of said rotary head cylinder when said long play mode is specified, wherein N is an even number. The magnetic recording/reproduction apparatus according to claim 1, wherein said tape speed control means comprises a capstan motor (10), and driving means (12) for controlling the rotation speed of said capstan motor according to a mode specified by said mode specifying means. A magnetic recording/reproduction apparatus according to claim 1, wherein said signal processing means comprises means for converting data to be recorded into a plurality of data blocks in time sequence, each corresponding to one track on a magnetic tape, when said standard play mode is specified, and for converting said 1/N compressed data to be recorded into a plurality of data blocks in time sequence, each corresponding to a 1/N track on a magnetic tape, when said long play mode is specified. The magnetic recording/reproduction apparatus according to claim 1, wherein said head control means comprises first and second switching means (22, 23) provided between said signal processing means and said pair of magnetic heads, pulse generation means (16, 18) for generating pulses in synchronization with rotation of said rotary head cylinder, timing control means (24) reponsive to said pulses and a mode specified by said mode specifying means for closing and opening said first switching means with one rotation of said rotary head cylinder as one period when said long play mode is specified, and head selection means (25), for opening and closing said second switching means, for alternately distributing said plurality of data blocks as record data of 2 channels to provide the same to said pair of magnetic heads for every one rotation of said rotary head cylinder in response to said pulses when said standard play mode is specified, and for alternately distributing said plurality of data blocks in N blocks as record data of 2 channels to provide the same of said pair of magnetic heads for every N rotations of said rotary head cylinder in response to said pulse when said long play mode is specified. The magnetic recording/reproduction apparatus according to claim 1, wherein said N is set as N = 2, and said magnetic tape is wound around said rotary head cylinder by 180° for travel.

Inventors: HAMAGUCHI TOSHIHIDE, MAEGAWA YOSHIKAZU, HAMAGUCHI, TOSHIHIDE, MAEGAWA, YOSHIKAZU
Applicants: SANYO ELECTRIC CO, SANYO ELECTRIC CO., LTD.
Application year: 1994
Main classification: G11B15
IPC codes: G11B15, G11B5, G11B20